Development of asynchronous motor test bench system

Abstract: This paper introduces an electrically enclosed energy-saving asynchronous motor test bench system, focusing on the system composition, working principle, characteristics and energy-saving effect.

Keywords: Electric closed energy-saving asynchronous motor test bench system

Chinese Library Classification Number: TM34 Document Identification Code: A Article Number: 0219-2713(2000)09-464-02

1 Introduction

Asynchronous motors have the advantages of simple structure, convenient manufacturing, use and maintenance, reliable operation, light weight and low cost, so they are the most widely used and demanded among various motors. About 90% of various electrical transmissions are driven by asynchronous motors, and asynchronous motors account for about 60% of the total load of the power grid. In order to meet the supporting requirements of various mechanical equipment, there are many series, varieties and specifications of asynchronous motors. With the continuous emergence of various new specifications of asynchronous motors, the design and production units of motors have also put forward higher requirements for the performance test equipment of asynchronous motors. The asynchronous motor test equipment introduced in this article uses the electric closed feedback method to test the efficiency, torque, temperature rise and other parameters of the asynchronous motor under various frequencies and different loads. Since this electric closed feedback method only needs to compensate for the loss of the test unit, this test equipment saves electricity. Compared with traditional mechanical loads, hydraulic dynamometer loads, and resistance energy consumption loads, the energy saving effect is 50% to 80%, which is an ideal asynchronous motor test equipment.

2 System composition

The system composition block diagram is shown in Figure 1.

(1) The main engine system mainly consists of two 400kW Z4 series DC motors M1 and M6, two 480kW synchronous generators M2 and M5 (the maximum frequency of the generator output voltage is 60Hz) and two asynchronous motors M3 and M4 (one is the motor under test and the other is the accompanying motor for testing). The DC motor M1 and the synchronous generator M2, the asynchronous motors M3 and M4, and the DC motor M6 and the synchronous generator M5 are connected through flange shafts.

(2) The power supply control system mainly consists of the AC incoming line switch DW15, the AC incoming line reactor L, the DC motor speed control system SCR1, the excitation systems SCR2 and SCR5 (independent weak magnetic system) of the two DC motors, the excitation systems SCR3 and SCR4 of the two synchronous generators and the relay operation circuit.

(3) Various voltage meters, current meters, power meters, frequency meters, thermometers, thermocouples, torque meters, etc. are used for motor test measurements. Users with conditions can also configure an industrial control computer and a printer to sample, calculate, and store various data during the motor test, and print out various data tables and characteristic curves.

3 System Working Principle

The thyristor speed control device SCR1 adjusts the speed of the DC motor M1 to change the frequency of the output voltage of the synchronous generator M2. The strength of the excitation current of the synchronous generator can be adjusted to change the size of its output voltage, and the strength of the excitation current of the DC motor M1 or M6 can be adjusted.

Figure 1 System composition block diagram

The one with weaker excitation current can be made to work in the motor state, while the one with stronger excitation current can be made to work in the generator state. Then, a voltage difference is formed between the armatures of the two DC motors, and current passes through. The greater the voltage difference, the greater the current. In this way, the energy in the armature of the DC motor working in the generator state is fed to the armature of the DC motor working in the motor state to realize the feedback of electrically enclosed energy. If M1 is made to work in the motor state and M6 is made to work in the generator state, then M2 is made to work in the generator state. At this time, M3 is the motor under test and M4 is the accompanying motor under test. On the contrary, if M6 is made to work in the motor state and M1 is made to work in the generator state, then M4 is the motor under test and M3 is the accompanying motor under test. Therefore, this test bench system is a reversible two-way operation system, so that the performance parameter test of two asynchronous motors can be easily realized at one time, reducing the number of electrical connections and mechanical connections, and effectively improving the work efficiency. During the test, the motor under test and the accompanying motor under test should be asynchronous motors of the same model and parameters.

4 System Features

The power control part of the test bench system adopts the power unit structure, the control system is an internationally popular large-board structure, and the control circuit is integrated and digitalized. The relay control of the entire system adopts a small PLC (Programmable Logic Controller), which has fault self-diagnosis and protection functions, and the relay operation and whole machine protection functions are perfect. The DC motor speed regulation part adopts a speed, current, and voltage three-loop control system. The digital signal output by the photoelectric encoder coaxially connected to the DC motor is used as a speed feedback signal to ensure the speed regulation accuracy of the whole machine, thereby ensuring that the frequency accuracy of the synchronous generator output voltage meets the accuracy requirements of the power frequency required by the asynchronous motor test. The voltage inner loop is added to ensure the stability of the system in the low-speed section, thereby ensuring the frequency accuracy of the low-frequency section, creating good test conditions for the test of AC variable frequency motors.

5 Conclusion

This test bench system is easy to debug and use, easy to change the frequency, stable and continuous loading, and can perform light load or full load tests on various types of asynchronous motors below 400kW, and has obvious energy-saving effects. After more than three years of actual operation on site, significant economic benefits have been achieved. With my country's reform and opening up, many motor manufacturers have set their sights on the international market, and the power grid frequency in many foreign countries is 60Hz, which requires the rated operating frequency of exported motors to be the same as that of foreign power grids. However, my country's power grid frequency is 50Hz, so the original test bench systems of many motor manufacturers are no longer able to meet the new requirements, and this test system can easily test the performance parameters of asynchronous motors or variable frequency motors with a rated frequency of 60Hz.

If the unit between the DC motors M1 and M6 of this system is replaced by a set of shaft-to-shaft connected gearboxes of the same type, a mechanical transmission product performance test bench can be formed, which can conveniently perform loading tests on the gearboxes to test their temperature rise, noise, torque and other parameters under various loads. Therefore, this test system has a wide range of application prospects.